Read your rules. You don't specify HOW the value of $x[0] is changed :-) vis Create an array @x such that changing $x[0] also sets $x[1] to the same value While assignment is one way to change a value....

@x=(\$_,\$_);
$_=10;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
$_=20;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
__DATA__
$x[0] = 10
$x[1] = 10
$x[0] = 20
$x[1] = 20
[download]

Create an array @x such that changing $x[0] ...

@x=(\$_,\$_);
my $initial_value = $x[0];
$_=10;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;
$_=20;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;
[download]

You're really printing the wrong thing.

print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
                 ^^      ^
LHS is $foo, RHS is $$foo. The output is very misleading.

print "\${\$x[$_]} = ${$x[$_]}\n" for 0..$#x;

LHS is $$foo and RHS is $$foo. But we're interested in $foo.

print "\$x[$_] = $x[$_]\n" for 0..$#x;

LHS is $foo and RHS is $foo. Output is correct and shows that the need
+ed change did not happen.
[download]

You're changing the variable that is refered to by the references in $x[0] and $x[1], but you're not actually changing the value in the container that is named $x[0].

Clearer would be: "so that assigning to $x[0] also changes ...", but as said, we're against sanity.

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }

I agree that it was not what was expected but it does fulfill the criteria as stated. The answer was probably supposed to be this as noted elsewhere:

$[

The index of the first element in an array, and of the first character
+ in a substring. Default is 0, but you could theoretically set it to 
+1 to make Perl behave more like awk (or Fortran) when subscripting an
+d when evaluating the index() and substr() functions. (Mnemonic: [ be
+gins subscripts.) 
As of release 5 of Perl, assignment to $[ is treated as a compiler dir
+ective, and cannot influence the behavior of any other file. --> Its 
+use is highly discouraged :-)


$[ = 1;
$x[0] = 1;
show();
$x[0] = 2;
show();
$x[1] = 3;
show();
sub show { print "\$x[$_] = $x[$_]\n" for 0..$#x; }
[download]

cheers

tachyon

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